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By J. Kinkead, R. M. Sherman, E. M. Frizzel

A recent research study performed under US Bureau of Mines Contract No. J0199088 "Modular Irrigation Equipment for Reclaimed Strip Mined Lands" investigated the feasibility of irrigation as a reclamation tool in the arid and semi-arid regions of the Western United States. Review of mined land characteristics, evaluation of irrigation systems, and assistance from the mining industry resulted in the design of two strategies for the implementation of reclamation irrigation using solid set systems. It is not the intent of this paper to suggest the generalizations made on the basis of a six state area can extend to the design of an irrigation system for a specific mine site. The purpose is to present two irrigation strategies that may be implemented with solid set irrigation in this six state area. The reader should note that the following is the result of research and, therefore, original concepts were presented. The ultimate validity of these concepts will be determined by future field tests.

Jan 1, 1983

By C. J. Fleisch, C. P. Clingerman

THE recent installation of a combination dust catcher, gas washer and precipitator at Carrie blast furnaces of the Homestead Steel Works has given very satisfactory results. The following description of the gas-cleaning installation is based on actual operating experience. When Carrie blast furnace No. 3 was rebuilt the decision was made to fine-clean all the gas produced by the furnace, because the management wanted fine-cleaned gas for fuel in the stoves and boilers. In order to keep the installation cost as low as possible, the gas-cleaning system was streamlined. All by-pass lines and goggle valves for bypass lines were eliminated from the system. A radical departure from the use of 8-in. tubes in the Cottrell-type precipitators was made by using 12-in. diameter tubes in a single compartment, the single compartment being divided into two units by a single partition wall in the top header. THE FURNACE PROPER A few of the characteristic points and dimensions of the furnace proper are: [Hearth diameter 26 ft. o in. Bosh diameter 29 ft. 1 3/4 in. Stock-line diameter 20 ft. o in. Large-bell diameter 114 ft. 8 in. Small-bell diameter 6 ft. 6 in. Height of furnace from center of iron notch to bottom of large bell, closed 94 ft. 4 in. Height of furnace from center of iron notch to main platform 105 ft. o in.] The furnace top is equipped with a McKee revolving distributor, the operation of which is electrically interlocked with the skips, bell hoists, and coke-weighing and charging apparatus through a Freyn automatic charging control. The gas leaves the furnace first through four offtakes, 5 ft. g in. in diameter, then through uptakes that are approximately 85 ft. high, which feed into a single down-comer that is 9 ft. in diameter. DUST CATCHER The primary dust catcher installed (Fig. I) may be described as a single-cone type. The inlet pipe at the top of the dust catcher is g ft. in diameter; it is flared to a conical shape as it extends down inside the dust-catcher shell, which is 35 ft. in diameter, 37 ft. high on the straight side, and has a conical top and bottom. The slope of the bottom is 50° with the horizontal. The cone-shaped pipe inside the dust-catcher shell is 42 ft. high and is 19 ft. 7 in. in diameter at its bottom lip where it releases the gas in-

Jan 1, 1943

By W. E. Pugh

The object of the following is to discuss a few of the problems encountered in the practical field application of reflection seismology. Very little has been published on this phase of the work and it is to be hoped that discussions will be presented by many seismologists who have met with these problems in the field. No attempt will be made to discuss the general principles of reflection prospecting, nor to outline the general field procedure. These phases have been presented more or less in detail in previous publications1 while economy of space and time prevents their being repeated or amended here. If, in the following pages, some criticism is offered of those who have already given their time and efforts to present valuable papers on reflection shooting, we trust that it will be accepted in the constructive light under which it is offered. We do not wish to give the impression that the following paragraphs represent ultimate achievement in field procedure; they are presented more to illustrate methods we have found satisfactory thus far. We believe that the following three subjects are inexorably linked with the continued future successes and more widespread use of the reflection method which, at the present time, is the most

Jan 1, 1934

By J. B. Scott, J. S. Nelson, G. H. Kruse, W. S. Johnson, K. L. Zerneke

The economics of pressure tunnel design emphasize the utmost utilization of the least expensive pressure-resisting material available, namely, the rock surrounding the tunnel. A major difficulty in the design is the problem of transferring internal hydraulic pressure to the rock through a tunnel lining or membrane provided to maintain watertight conditions. The lining is necessary not only to prevent water loss, but to prevent the diffusion of water at high pressure through joints and fractures beyond the confines of the tunnel, an occurrence which could ultimately affect the stability of the rock mass through which the tunnel passes. Because of its toughness and ability to bridge localized areas of weakness, steel is used for a lining material whenever high internal pressures are involved. The steel lining is coupled to the surrounding rock mass through an annular ring of concrete backfill. It is paradoxical that the steel lining, needed primarily to assure water tightness, must of necessity be incorporated into the structure as a major pressure-resisting component, not to augment the bearing capacity of the concrete and rock, but to limit the strain for the safety and preservation of the steel lining itself. With the deformation modulus of the steel so much greater than that of the rock, the liner approaches its yield strength before the load capacity of the rock can be fully mobilized. An economical determination of plate thickness for steel liners is therefore dependent upon measurement of the properties of the surround-

Jan 1, 1970

By Frances Hurd

WHEN 60:40 brass is heated to 825° C., given a drastic quench to obtain the beta solid solution, and reheated, various changes take place in the structure. Reheating at 200' C. causes a fine, granular, sorbitic structure to appear which has been considered alpha solid solution. These particles coalesce at higher temperatures of reheating, and at 470° C., the alpha forms twins. A further study of these transformations was considered worth investigating.

Jan 1, 1927

By J. F. Smith

ELASTIC constants of yttrium and eleven of the rare earth elements have been measured. This has been accomplished by measuring the propagation velocities of ultrasonic pulses. The velocity measurements were made by noting the elapsed time between an applied pulse and the appearance of successive echoes. The pulse-echo technique has become relatively common, and the basis of the measurement is outlined in several standard tests, e.g., Heuter and Bolt.1 Two important assumptions are made when using this method for the determination of elastic moduli. First, the pulse is assumed to propagate as a plane wave. To justify this assumption, the cross section of the test specimen should be large compared to the wave length of the transmitted pulse. For these measurements on the rare earth elements the minimum cross section wave length ratio was about 20. A second assumption which must be made when using polycrystalline specimens is that the grains are sufficiently numerous and randomly oriented so that the specimen may be approximated as elasti-cally isotopic. The grain size in the as-cast specimens which were used is believed to be sufficiently fine for this approximation, and the degree of preferred orientation is believed to be small. Supporting this viewpoint is the fact that elasticity measurements by the pulse-echo technique on as-cast specimens of other metals give results which are in satisfactory agreement with values obtained by other techniques. Hence, it is believed that the measured elasticity values for the rare earth elements are not apt to be seriously in error due to the assumption of elastic isotopy. The apparatus used in this determination was a modified Sperry Reflectoscope with a precisely calibrated time base circuit. Piezoelectric transducers were used both to generate the pulse and to detect the echoes. X-cut quartz crystals were used for the longitudinal modes, and Y-cut quartz crystals were used for the shear modes. Frequencies of 2.25 and 5 megacycles per sec were employed. Most of the specimens were 2.5 to 5.0 cm in length. Results Table I is a tabulation of the measured propagation velocities of longitudinal waves and of shear waves, together with densities obtained by Sped- ding, Daane, and Herrmann2 from lattice parameter measurements. The shear modulus, Poisson's ratio, and Young's modulus were calculated from the data in Table I through use of the following relationships: µ = pv32 [1] s=2-(vb/vs)2/2[1-(vb/vs)2] [2] and Y= 2µ(l+s) [3] where s is the shear modulus, Y is the Young's modulus, s is Poisson's ratio, p is the density, V0 is the longitudinal wave velocity, and v, is the shear wave velocity. The calculated quantities are shown in Table 11. Compressibility values can be computed from the relationship and the computed values may be compared with measured values obtained by Bridgman.8 Table III lists the data for such a comparison. The agreement is satisfactory, being particularly good for neodymi- um and gadolinium, poor for samarium, and intermediate for the other elements. Some variation is expected since Bridgman's measurements are isothermal, whereas the present measurements are adiabatic. In addition there may be some effect due to small variations in purity. Though most of the rare earth metals measured by Bridgman and all of the metals used in the present measurements were prepared at this laboratory, minor purity variations might exist since the samples came from different lots. Also, any imperfections such as dislocations, vacancies, voids, grain boundaries, microcracks, etc., should contribute to the volume change of a com-

Jan 1, 1958

By Frederick K. Allgaier

As part of an ongoing research program, the Bureau of Mines, U.S. Department of the Interior, is monitoring surface subsidence over six longwall panels at three Utah coal mines. These sites are characterized by mining depths of 244 to 610 meters (800 to 2,000 ft .), thick and massive sandstone layers in the overburden strata, multiple seam mining, extraction heights of approximately 1.8 to 3 meters (6 to 10 ft.), and rugged surface topography. Maximum subsidence, angle of draw, timing relative to mining, horizontal strain, and rate of subsidence development are being determined and correlated with mining and geologic variables. Results to date indicate the maximum vertical subsidence over the monitored panels ranges from 0.6 to 0.9 meters (2 to 3 ft.). The major factors controlling the amount of subsidence are the panel dimensions and the status of adjacent panel mining. Only minor surface cracking at the panel ends was evident at any of the sites. In all cases, there was a time lag of several months between the start of mining and subsidence at the surface. As subsequent panels are monitored and additional data become available, better estimates of the effect of various site characteristics on the subsidence will be possible. Ultimately, improved prediction capabilities will allow mine operators in the West to evaluate the potential for subsidence-related damage which could affect the current or future land use above the mine.

Jan 1, 1982

By J. M. Bugbee

THE engineer and the conservationist agree that effective water drive is the desirable reservoir production mechanism. Water drive may result either from the expansion of edge water, the reservoir water bordering an oil pool, or from the artesian flow of edge water from the outcrop. Thus, the extent of the reservoir has an important bearing upon both the rate and the ultimate quantity of water influx to an oil pool. Lens-type reservoirs are generally recognizable, but the complete structure of the more important domal types, having possible limitations from crestal and synclinal faulting, is not well understood. The delineation from cores, electrical logs and exploitation phenomena of the crestal portions of reservoirs is increasingly exact. This paper suggests that inference from these factual pictures, combined with the scattered well and geophysical data of the synclines and with consideration of the dynamics of structural formation, may be applied to solving the complete geologic structure. Since faulting on the domes and in the synclines may effectively seal and thus limit the size of a reservoir and bar additional water influx, consideration of geologic structure and its possible effects is essential to complete analysis and prediction of reservoir performance.

Jan 1, 1942

By R. W. Waterfill

MANY existing ore deposits of valuable metals have been worked out in their upper surface levels and the continued productivity of these mines is dependent on their extension to greater depths in the earth. The maximum depths at present reached are about 6000 to 8000 ft. below the surface, with no evidence of an impoverished ore vein. These mines are widely distributed; some of the best known are in South Africa, Brazil, India and in the western sections of the United States. Among the factors which increase the difficulty of working these mines at increasing depths are hoisting, rock pressure and temperature. The manner and effectiveness with which these problems are met will, no doubt, determine in a large measure the ultimate depths to which any mine can be profitably worked. The most critical of these three factors at present is the increase in temperature with depth. The high temperature and humidity in many of these mines at present is severely detrimental to the health of the workers and greatly hampers their efficiency. Some have almost reached a condition in which the human system cannot survive. The problems involved in the cooling and ventilation of mines have all been ably analyzed and presented in previous articles. For this reason, only a resume of conditions affecting the cooling and conditioning of deep and hot mines will be given in this paper before attention is directed to possible methods of improving atmospheric conditions in the working levels.

Jan 1, 1929

By W. F. Brace, James D. Byerlee

Although prediction of failure of rocks may be ultimately possible without knowing in detail how failure occurs, understanding of this process is certainly of fundamental interest in rock mechanics. Of the various failure mechanisms, probably brittle fracture is of greatest interest. Recent reviews have brought this subject nearly up to date (Hock,1 Price,2 and Jaeger 3) and here, we summarize certain recent developments. As our understanding of brittle fracture is derived almost solely from laboratory studies this will amount to a review of certain laboratory experiments. New studies in four areas are pertinent; these concern 1) the volume changes which accompany brittle fracture, 2) the propagation of cracks in compression, 3) certain frictional characteristics of rocks and minerals at high pressure, and 4) the law of effective stress for crystalline rocks. Our objective here is less to present an entirely consistent, complete picture of how a rock fractures than it is to emphasize gaps in our understanding and, thus, suggest areas that need further study. Progress is still painfully slow in this field and perhaps this approach will stimulate new work. OBSERVATIONS Although the behavior of large rock masses is most often the concern in rock mechanics, the number of large-scale experimental tests is still vanishingly small. Our experimental observations arc, by and large, still made on small, relatively flaw-free, rock samples. Here also we report the behavior of small samples.

Jan 1, 1967

By Arthur Phillips, C. H. Mathewson

During the past year considerable work dealing with the mechanical properties and microstructure following the anneal under uniform condi-tions of certain types of commercial rolled brass has been done in this laboratory. Since these experiments were conducted with the active cooperation of the Bridgeport Brass Co., involving free use of its product, and have thus furnished information which is characteristic of some of its special mixtures, full publication of the numerical relationships and comparative results encountered does not seem justifiable. Some of the more general features of this work are, however, available and it is our present purpose to use the material in question, along with some results of special tests, in discussing the characteristics of recrystallization as related to the degree of hardening by strain and the ordinary annealing variables. We desire to make acknowledgment of the many courtesies extended by Mr. Charles Ferry, Metallurgist of the Bridgeport Brass Co., and the value of his cooperation, which has greatly stimulated the study of brass in this laboratory. A clear and systematic presentation of the principal relations between temperature and time of anneal, the changing physical properties and microstructure and the degree of previous reduction by cold-rolling, was first made, in the case of rolled brass and copper, by the French engineer, C. Grard,' in 1909, although much fragmentary information of this general character had appeared earlier and the main facts involved were undoubtedly known to many brass specialists through their own private research. From this work, it appears that in the cartridge mixture (67 per cent. copper, 33 per cent. zinc) the properties imparted by cold-working within the limits, 13 to 75 per cent, reduction of area by rolling Original Area — Final Area 0.13 to 0.75), are not affected by anneal- Original Area " ing for a 50-min. period at any temperature below 200°C. At or in the

Jan 1, 1916

By Michael B. Gross

A numerical study of the vulnerability of unlined tunnels in jointed rock has been performed with the STEALTH computer program, using the CAVS model for jointed rock. CAVS, for Cracking And Void Strain, is a constitutive model that can simulate the initiation/propagation of fractures and the slip along fracture planes in a jointed rock mass. The CAVS model is unique because it represents a spatially oriented approach to rock failure, rather than the traditional invariant formulation, and because the CAVS submodels for slip friction and slip-induced dilatancy are used to represent the weakening influence of joints, rather than applying ad hoc modifications to the elastic moduli of the host rock. The CAVS model, as embedded in the STEALTH computer program, has performed numerical simulations of tunnel collapse at high overstress levels. These calculations show that the ultimate strength of the tunnel depends strongly on the joint properties, and that the results of the calculations are in qualitative agreement with the observed data for collapse of a tunnel in tuff.

Jan 1, 1984

By Phillip O. Tyree, Joseph W. Mussey

Bio-epigenetic sulphur deposits occur in Pecos, Reeves and Culberson Counties of far West Texas. Sulfate reducing bacteria, utilizing hydrocarbons as energy, transformed gypsum into replacement limestone and hydrogen sulfide. Hydrogen sulfide, retained in the pores of the replacement limestone, was subsequently oxidized by highly oxygenated groundwaters, and native sulphur precipitated. West Texas sulphur was first recognized at surface exposures by William P. Blake, a geologist attached to the Captain Pope Military/ Scientific Expedition of 1854. Attempts were made in the early 1900's to mine these sulphur vent exposures by a retort method, but the ventures met with little success. In 1967, Duval discovered a large sulphur deposit near some of the old sulphur works in Culberson County. Duval also expanded reserves in a small sulphur deposit in Pecos County. The Frasch process, developed for producing sulphur from Gulf Coast salt domes, proved successful in West Texas type sulphur deposits also. However, modifications of the process were necessary to provide economical and efficient sulphur recovery from the varied ore occurrences. West Texas conditions and logistics require the ultimate in productivity to be competitive in the domestic and foreign sulphur markets. Several companies, in addition to Duval, are producing or have produced sulphur in West Texas. As of June 1, 1984, a total of 29.87 million mt (29.4 million long tons) of sulphur had been produced west of the Pecos River. Duval Corporation has produced more than 88 percent of that total.

Jan 1, 1985

By C. V. Millikan, Herbert F. Beardmore

Declining Productivity Index, as considered herein, is a productivity index that has a substantially and consistently decreasing value when measured over a period of a few hours. If not recognized, it may be interpreted as representing an unsettled or unstable condition in a producing well. It forms the basis of a number of predictions as to future performance compared with the performance of wells in which the productivity index does not decline. The nost important of these are that: (I) the rate of oil production will decline more rapidly, (2) the gas-oil ratio will usually increase abnormally, (3) the amount of water ultimately produced will be negligible, if any, (4) stop-cocking will increase current production and decrease gas-oil ratio. When such relative well performance is indicated, it follows that certain reservoir performance and operating practices may be anticipated: (I) disappointing recovery, (2) longer natural flow, (3) no active water drive, (4) better evaluation of acidizing, shooting and reworking, (5) intermittent operation of wells, (6) smaller pumping equipment required. It is significant that the basis of these important predictions is bottom-hole pressure tests that can be made immediately after completion of the wells. Introduction "'Productivity index" is the number of barrels of oil produced per day per pound per square inch of differential pressure between the reservoir and the bottom of the well. "Declining Productivity Index," as considered herein, is a productivity index that has a substantially and consistently decreasing value when measured over a period of a few hours. Productivity index can be determined only when the rate of production can be stabilized. In most wells the rate of production and bottom-hole pressure are easily stabilized to give a constant productivity index for a period of many hours. A few produce so erratically as to preclude probability of an acceptable test in the usual sense. A satisfactory productivity index can be determined in some wells only by gauging the production accurately by hours, measuring the bottom-hole pressure continuously, and from these data calculating the productivity index for successive hours. Such figures frequently will have a decreasing value—that is, a declining productivity index—and when plotted on double. logarithmic cross-section paper with productivity index as ordinate and time as abscissa will be a straight-line curve. The angle between the curve and the abscissa is referred to as the rate of decline. Declining productivity index may appear to be the result of change in permeability to oil due to decreasing saturation of oil and increasing saturation of gas in the reservoir. It is possible that such is in fact the cause, but if so, more is involved than merely relative saturation of oil and gas. This seems evident because the rate of decline in productivity index is substantially the same regardless of the pro-

Jan 1, 1945

By Read Winterburn

This study of the relationship of the accumulation and drainage of oil to the structural conditions in the Wilmington oil field is presented with the hope that the data contained herein will aid in efficient exploita-tion of other fields where similar conditions exist. It is also probable that the conditions observed in this field will enable accurate comparisons of various well-spacing programs as to efficiency of production and ultimate recovery. Formations in Wilmington Field Age Formation Thickness Lithology and Remarks Quaternary and Pleistocene. San Pedro 1000 t Fresh-water sands, gravels and clays Pliocene Upper Pico 800 t Alternating sands and silt- Stones Pliocene Middle Pico 0-200 ± Sands and siltstones Unconformity Pliocene Repetto 875-1150 Gray and green shales, silt-stones and sands at top grading to interbedded gray-ish brown shales and fine-grained sands toward bot-tom Miocene Puente 4100± Hard brown shales and sands. Sands are fine and uncon-solidated at top, becoming firmer and coarser grained toward bottom. Top por-tion contains layers of lam-inated diatomaceous shale Unconformity Schist The data included herein are not complete as to all areas and zones, being confined mostly to the area south of Anaheim Street. The sections presented are illustrative of edge-water conditions in the Terminal zone and Tar zone, but have not been extended down the structure far enough

Jan 1, 1940

By J. C. Konopka, S. A. G. Poppen, E. K. Roesner

Many shafts have experienced stability problems during shaft sinking because the designer failed to fully appreciate the conditions he would encounter. Some shafts have failed during construction because the ground supports provided to compensate for the expected conditions were inadequate despite the most careful investigations and analyses. To design a ground support which is ultimately safe to achieve stability during shaft sinking would be too costly and impractical and, therefore, many shafts would simply not be constructed. The design of a ground support for shaft sinking based on an intimate understanding of the expected ground behaviour and stress development during excavation combines the art of mining with the science of geotechnical engineering. Where no historical design data is available, the designer of the ground support must: 1. classify the rocks and soils and assess their behavioural characteristics; 2. calculate the primary and secondary stresses; 3. design and/or select a ground support system which will ensure stability of the excavation during shaft sinking.

Jan 1, 1983

By Gordon M. Matheson, Charles V. Logie

The current state-of-the-art design of mine pillars can be grouped into empirical and numerical design techniques. Numerical design techniques are based on sophisticated computational techniques which analyze the stresses and strains through the interstices of a pillar. Empirical techniques are less exact, but have been widely used, particularly for coal mine pillar design, because of their ease of computation. Over the years numerous empirical equations have been proposed to calculate the ultimate strength of coal mine pillars. This paper presents a review of the various equations which are most frequently utilized and examines the fundamental assumptions, limitations and applicability of the design formulae. The review intends to provide the practicing mining engineer with an understanding of the assumptions and mathematical basis of each equation to aid in the selection of the criteria most applicable to his specific design problems. Recommendations are made of the empirical equations that are presently most acceptable for design.

Jan 1, 1983

By Carl D. Broadbent

In 1956, Kennecott Copper Corp. instituted a slope mechanics program. Its objective was to obtain effi-ient and safe pit slopes. Since then, Kennecott has onducted a great deal of research into the area, most otably at the Kimbley Pit. This paper, which describes the transitional work at this period and draws from the pertinent experimental work done by others, paves the way for the next step of the program: refining the design process and applying it for profit. The goal of slope mechanics is to achieve efficient and safe pit slopes. In the case of ultimate mine slopes, the objective is to minimize the stripping ratio by steepening the slopes to their maximum stable limit. On the other hand, the inclination of working slopes is normally established by operating space requirements and the function of slope mechanics should be the continuous surveillance of slope conditions to assure long-term stability and provide timely warning of impending slides so that corrective measures may be incorporated in production planning. In 1956, Kennecott instituted a program to provide

Jan 1, 1970

By Donald E. Crowell

In the fall of 1969, ASARCO and Newmont Mining Co. began the design of the 700tpd concentrator at their Black Cloud shaft located near Leadville, Colo. The concentractor would treat by flotation a Pb-Zn-Ag ore containing minor gold values. Flowsheet design was based on laboratory test work performed at the Minerals Research Testing Laboratory of ASARCO. Since the concentrator is located at an elevation of 11,000 ft, cold weather was a major factor in design considerations. The original capacity was designed as 700 tpd but for various reasons an ultimate capacity of 1,000 tpd was desired. This necessitated special consideration in the design of several areas, particularly the grinding circuit. The grinding circuit chosen was a single 9 X 12 ball mill operating in closed circuit with one 20-in. cyclone. The ball mill will operate at low speed and as an overflow type originally. The mill can be speeded up and converted to grate type for handling the larger tonnage when required. Thickeners and filters were oversized and space was left for additional flotation cells in order to handle the increased tonnage in these areas. Pumps were sized so that they could handle the increased tonnage by increasing their speed. Construction began in May 1970; the Black Cloud concentrator went on-stream in April 1791.

Jan 1, 1974

By Leslie F. Tedsen, Alan E. Flanigan, John E. Dorn

IT is necessary occasionally to use aluminum-alloy sheet where moderately elevated temperatures are encountered. Considerable attention has been directed toward determining the influence of "artificial aging" on the room-temperature properties of the precipitation-hardenable alloys, as testified by numerous company reports and by references 1 to 4. Investigations on the properties at elevated temperatures are few, however,5-7 and have not always covered the range of times and temperatures of greatest interest. The present investigation was instituted to overcome this deficiency. The work was done for the Office of Production Research and Development of the War Production Board, under the supervision of the War Metallurgy Committee, as a part of the "restricted" Project NRC-548. It has been released for publication by the Office of Production Research and Development. As is well known, the high-strength aluminum alloys achieve their remarkable properties as a result of precipitation-hardening. In production they are subjected to a solution heat-treatment followed by quenching, to retain the supersaturated solid solution. The solution treatment is followed by "aging" (precipitation-hardening) either at room temperature or at a suitable elevated temperature. A considerable increase in tensile and compressive yield stresses results from precipitation at room temperature ("natural aging"). Through the elevated-temperature process ("artificial aging") it is possible to obtain values of yield stress considerably higher than those attainable by natural aging. The increase in yield stress is accompanied by a smaller gain in ultimate tensile stress and by a decrease in elongation. During [TABLE I.-Sources of Materials Used in the Testing Program MATERIAL ORIGIN AND TREATMENT 24S-T Alclad.... From Lockheed stock. 24S-RT Alclad... Direct from mill. 24S-T80 Alclad.. 24S-O Alclad from Lockheed stock, solution-heat-treated (925°F., water quench) and aged at 375°F. for t0 t % hour. 24S-T8I Alclad.. 24S-T Alclad from Lockheed stock, plant stretched up t0 I per cent and aged t0 ± % hr. at 375°F. 24S-T86 Alclad.. 24S-RT Alclad from Lockheed stock aged 534 ± 34 hr. at 375°F. 6IS-W (bare).... From Lockheed stock. 6IS-T (bare) 6IS-W (bare) from Lockheed stock aged 8 hr. at 350°F. XB7SS-T Alclad. From Lockheed stock.] the first stages of artificial aging the yield stress increases steadily until it reaches a maximum value. In this condition the material is said to be "fully aged." Further exposure results in "overaging," attended by a steady decrease in yield stress. In the production of the artificially aged materials, temperatures and times are selected to achieve full aging. The following important characteristics are associated with the process: I. The higher the temperature, the more rapidly is the fully aged condition attained.

Jan 1, 1945